1. Field of the Invention
The present invention relates to a light emitting diode device having a nanocrystal-metal oxide composite and a method for fabricating the same. More particularly, the present invention relates to a light emitting diode device having improved luminous efficiency and stability, and a method for manufacturing the same.
2. Description of the Related Art
In general, a light emitting diode (“LED”) has advantages such as being compact and having excellent monochromatic peak wavelength and light efficiency, for example. Thus, the light emitting diode is widely utilized as a light source in various display devices. Further, the light emitting diode has been actively developed as a high efficiency, high output light source which can replace a backlight of a lighting device and other display devices.
LED devices are generally commercialized in a package including an LED chip having a cathode and an anode connected thereto, an epoxy mold layer formed by uniformly coating a phosphor onto a surface of the LED chip, and a packing material for sealing the device. A p-type electrode and the cathode of the LED chip are connected with a thin metal line. An n-type electrode of the LED chip is connected to a metal post, e.g., an anode lead. Furthermore, a hole cup is prepared in front of the lead frame to form the anode. The LED chip is disposed in the hole cup and connected as described above. The hole cup reflects light emitted from a light emitting side of the LED chip.
Recently, a fabrication process of a white LED, which has been developed for use as a light source for a lighting or display device, utilizes a method of mixing yttrium aluminium garnet (“YAG”) phosphor in a blue LED chip or mixing red phosphor and green phosphor to improve a color purity. However, when an inorganic phosphor is used as a luminescent material, it is difficult to obtain high efficiency and high color purity from the LED chip. Thus, a method having a semiconductor nanocrystal with various luminescent materials has been recently studied. The emissive and electrical properties are controlled by adjusting a size and/or composition, for example, of the nanocrystal. Moreover, the nanocrystal has advantages such as high efficiency and good color purity, making the nanocrystal attractive for use in light emitting devices such as an LED device, an organic electroluminescent device, a laser, holography or a sensor, for example.
In order to use the nanocrystal as a light converting luminescent material of an LED device, the nanocrystal dispersed in a solution state must be mixed with a polymer resin, for example, used in an encapsulation of the LED by applying a procedure similar to that discussed above for a conventional inorganic phosphor material. However, it is difficult to obtain a uniform dispersion of the nanocrystal in the polymer resin. Further, chemical damage, for example, causes defects on a surface of the polymer resin of the nanocrystal. As a result, degradation of the nanocrystal, such as a reduction of emission characteristics, occurs.
To reduce surface defects on the surface of the nanocrystal, a method for synthesizing the nanocrystal-metal oxide composite in a core-shell structure has been considered. However, even when the nanocrystal-metal oxide composite is prepared in the core-shell structure, a problem of a reduced efficiency due to chemical damage still exists. Further, a surface treatment procedure for improving dispersibility of the nanocrystal reduces luminous efficiency. Moreover, an organic substance used in the surface treatment may remain in the polymer resin, thereby causing other problems such as interrupting a curing process or reducing optical and thermal stability, for example.